1. Field of the Invention
This invention relates to an abrasive tape to be used for the polishing of a magnetic head, or the like. This invention particularly relates to an abrasive tape to be used for the rough polishing of a surface of a magnetic head, or the like.
2. Description of the Prior Art
Magnetic heads for video tape recorders or for high-grade audio decks are made by being polished with abrasive tapes. The abrasive tape comprises a flexible substrate, and an abrasive layer overlaid on the flexible substrate. The abrasive layer is overlaid on the flexible substrate by applying an abrasive composition consisting of abrasive grains, a binder, additives, and the like onto the flexible substrate and drying the applied layer of the abrasive composition.
In general, when the surface of a magnetic head, or the like, is to be polished with the abrasive tape, two reels are positioned with the magnetic head or the like intervening therebetween, and the abrasive tape is moved in contact with the surface to be polished between two reels. The abrasive tape is flexible and can snugly fit to a curved surface. Therefore, the abrasive tape is more suitable for the polishing of the curved surface of the magnetic head, or the like, than grinding wheels. Also, the abrasive tape can achieve scratch-free, accurate polishing of the surface to be polished, and is therefore indispensable to the finish polishing of a rough-polished surface.
As is well known, processes for polishing a magnetic head with the abrasive tape comprise a rough polishing process, with which the tip of the magnetic head is shaped into a desired form, and a finish polishing process, with which the surface of the magnetic head is polished to a smooth finish. In the rough polishing process, a rough polishing tape, which is suitable for the rough polishing, is used. In the finish polishing process, a finish polishing tape, which is suitable for the finish polishing, is used. As the finish polishing tape, polishing tapes disclosed in, for example, Japanese patent publication Nos. 53(1978)-44174 and 62(1987)10782 have heretofore been used.
The rough polishing tape, which is used to shape the tip of a magnetic head into a desired form, should have good polishing performance and should be capable of quickly shaping the tip of a magnetic head into a desired form. Also, the rough polishing tape should not deeply scratch the surface of the magnetic head.
If the rough polishing performance is bad, a long time will be required for a magnetic head to be polished, and therefore the productivity during the rough polishing process will become low. If the rough polishing tape deeply scratches the surface of the magnetic head, a long time will be required for the deep scratches to be eliminated during the subsequent finish polishing process, and therefore the productivity during the finish polishing process will become low. Also, larger amounts of polishing tapes will be required during the rough polishing process and the finish polishing process. This is not advantageous from the viewpoint of economy.
In order for the polishing performance to be improved, the diameters of the abrasive grains contained in the abrasive layer of the abrasive tape should be increased. On the other hand, in order that the abrasive tape does not deeply scratches the surface of a magnetic head, the diameters of the abrasive grains contained in the abrasive layer of the abrasive tape should be decreased. Therefore, the requirement with respect to the polishing performance and the requirement with respect to the elimination of the deep scratching of the surface of a magnetic head are incompatible with each other. Accordingly, one of the two incompatible requirements must have heretofore been sacrificed, or a rough polishing tape having intermediate characteristics must have heretofore been used. A rough polishing tape having satisfactory characteristics cannot be obtained merely by the control of the diameters of the abrasive grains. Japanese patent publication No. 62(1987)-10782 discloses a method wherein an abrasive layer is constituted of a mixture of hard abrasive grains Cr.sub.2 O.sub.3 and soft .alpha.-Fe.sub.2 O.sub.3 abrasive grains. With the disclosed method, the smoothness of a polished surface of a magnetic head can be improved. However, with the disclosed method, because the soft .alpha.-Fe.sub.2 O.sub.3 abrasive grains are used the polishing performance becomes markedly bad. Therefore, the disclosed method is not suitable for the rough polishing process.